The advent of modern scanning laser-based Raman spectrometers have allowed for increasingly sophisticated microstructural analysis with high spatial resolution. Fluorescence, long considered a nuisance in these measurements, is now being applied as a direct output signature from these experiments. Rare earth elements (REE) are particularly suited as probe ions for these experiments, being important fission products and having f-f transitions split by local crystal field, allowing investigation of localized phenomena such as partitioning and atomic environment. Laser excitation wavelength selection combined with limited bandwidth gratings makes certain ions highly sensitive to given experimental conditions (e.g., Pr³⁺: 455 nm light with 50-3500 cm^-1 grating, allowing investigation of 456-541 nm light; Sm³⁺, Dy³⁺: 532 nm light with 86-6000 cm^-1 grating, allowing investigation of 534-781 nm light; Nd³⁺, Yb³⁺: 785 nm light with 50-3500 cm^-1 grating, allowing investigation of 788-1054 nm light). In this talk, we will briefly summarize the physics of these experiments, then provide several examples of its use as applied to nuclear materials. Examples include glass-ceramics with multiple rare-earth containing phases, radiation damage in ceramics and natural analogues, and doping of fuels and fuel surrogates, as well as assessment of purity of raw materials. Though REE are particularly suited to these methods, investigation of other metals in various matrices is possible, such as the luminescent transitions of Cr³⁺ and its sharp R-line used in ruby lasers.

Positrons, after implantation into materials, rapidly thermalize and then annihilate with electrons. In the presence of vacancies and other open volume defects positrons trap there prior to annihilation. Conservation of energy and momentum leads to Doppler broadening of the annihilation line which carries information about the annihilation site. Combined with the use of variable energy beams this enables the identification and assessment of vacancies as a function of depth down to about 5 micrometers from the surface. Nuclear materials such as fuel elements, waste, or glasses for vitrification of such waste are exposed to energetic particle irradiation from fission products or self-irradiation of the nuclear materials. Defects including vacancies are generated and alter the material properties. Helium can accumulate as bubbles in voids. Point defects are generated. In this presentation I will discuss the benefits of positron annihilation spectroscopies in nuclear materials and what can be learned. Examples include recent work on the leaching of ISG glasses used for waste vitrification as well as defects generated by ion implantation into oxides and metals.

Various glass and ceramic waste forms have been proposed for high-level nuclear waste (HLW) immobilisation and geological disposal in countries such as the United Kingdom, United States and France. One of the major concerns related to geological disposal is the corrosion of the waste form due to groundwater inlet in these underground facilities and the role radiation damage has on the corrosion of these materials. In the literature, a limited amount of research has been performed on calculating the surface corrosion rate of these glass and ceramic waste forms, largely due to the lack of experimental techniques that can quantifiably measure the surface topography of the material in-situ during an aqueous corrosion experiment. Therefore, new, and novel state-of-the-art experimental techniques are required to study the surface corrosion behaviour of potential glass and ceramic host materials for HLW immobilisation. In this study, ceramic phases of Zirconolite and Perovskite (CaZrTi₂O₇ and CaTiO₃), a glass-ceramic material and a glass material (International Simple Glass 2) were irradiated using Xe²⁺ ions in the Microscope and Ion Accelerator for Materials Investigation (MIAMI-2) Facility at the University of Huddersfield. The samples were then corroded in aqueous solutions of deionised water and a one molar solution of NaOH with in-situ topographic measurements taken using High-Speed Atomic Force Microscopy (HS-AFM) and Interferometry to precisely study surface corrosion rates of these four different irradiated materials in different pH solutions. Post-corrosion TEM was additionally carried out on the corroded samples to offer complementary sub-surface measurements to the above-surface measurements provided by HS-AFM and Interferometry. These results therefore allow us to study both diffusion and dissolution during aqueous corrosion.

Several different types of ceramics have been proposed as potential candidates for the management of radioactive wastes/isotopes found at the back end of the nuclear fuel cycle. Long-term management of such radioactive wastes will involve encapsulation and geological disposal in a specifically engineered geological disposal facility (GDF). Self-irradiation damage, helium bubble formation, and corrosion in conditions typical of a GDF are expected to alter their physiochemical properties and corrosion potentially impacting the release of the radioactive elements into the biosphere. A fundamental understanding of the contribution of such factors towards the overall corrosion is thus an important part of the safety assessment and confidence building. In the majority of the cases, short-term experiments are conducted under controlled conditions on simple to complex model systems, and results are extrapolated to time scales more representative of the expected lifetime of the GDF (hundreds of thousands of years). Luckily, several of these synthetic materials have almost exact natural radioactive analogs, and their studies, both, in terms of their radiation response and weathering provide invaluable data and information for the validation of the short-term controlled experiments.

In this presentation we aim to present results from novel methodologies to study short-term corrosion in almost real-time and combine these with the studies of natural analogies, which have gone weathering for millennia, to develop a more coherent picture of how radiation damage and corrosion could affect the materials used for the conditioning of radioactive elements.